On 11/15/2018 10:33 AM, tamzikin@sina.com wrote:
Hi Marek,
Hi,
CC the list next time.
I am Kin, nice to meet you, I know you because I saw your u-boot video on Youtube. I am a learner of u-boot, and I have a big confusion on it, so I would like to find answer from you. For compiling, some platform have CONFIG_SYS_TEXT_BASE set to some value, and CONFIG_SYS_TEXT_BASE will be used when linking all sections into one u-boot, so it can be said that the address of the first instruction in u-boot will be bound to address CONFIG_SYS_TEXT_BASE, and every variable and function will also be bound to address based on CONFIG_SYS_TEXT_BASE.
Yes, that's the link address.
Before relocation, gd->relocaddr is calculated, and if gd->relocaddr doesn't equal to CONFIG_SYS_TEXT_BASE, u-boot is relocated to gd->relocaddr but not CONFIG_SYS_TEXT_BASE.
Right, U-Boot gets relocated to the end of RAM , so it's out of the way.
Since all the functions and variables are bound to address based on CONFIG_SYS_TEXT_BASE during compilation, so if we don't locate u-boot to CONFIG_SYS_TEXT_BASE, u-boot cannot reach functions and variable correctly.
Take a look at relocate_code function and search for R_ARM_REL32 for example, it should give you an idea how that relocation stuff works and how the function pointers get adjusted to match the binary location.
But this is actually how u-boot is designed, so I am confused, could you give me any hint for that? Thanks.